(30b) Risk-Analysis Based Flare Load Reduction During Ethylene Plant Upsets

Ethylene plant upsets usually lead to the flaring of off-spec products, resulting in significant raw material and energy losses, as well as air emission problems.  Under the premise of plant safe operation, establishing process recycles connecting off-spec streams to their upper-stream process can help ethylene plants reduce flare load during plant upsets.  In this paper, recycling two most significant flaring sources, effluents from the acetylene reactor and ethylene tower overhead, are addressed.  Operational strategies for recycling the potential flaring sources under various process upsets are developed and analyzed based on rigorous plant-wide dynamic simulations. Risk analysis on the performance of cracked gas compressor (CGC) system has been conducted through the quantitative comparison of the effectiveness of various recycling strategies.  Therefore, the study not only discloses how to effectively and efficiently design and operate recycling streams, but also addresses the CGC operating safety.  Case studies have demonstrated that the risk-analysis based flare load reduction strategies can proactively reduce the flaring emission amount and upset time, and therefore have great potentials to bring economical and environmental benefits to ethylene plants. The study is helpful in supporting ethylene plant decision-makings on handling plant upsets.